Pipeline and apparatus systems having pressure relief devices are conventionally used in spinning and extrusion systems in which the fluid forms the molding material to be spun. The fluid is normally transported through the pipeline system from a reaction tank, in which it is mixed from its individual constituents, to a spinneret or extrusion device by which it is molded into molded bodies, e.g. by being spun or extruded. In general, the pipeline systems include further apparatus such as pumps, pressure compensating tanks, sieve systems, or heating devices.
The fluids used in spinning facilities are heat-sensitive and tend to carry out a spontaneous exothermic reaction whenever a specific maximum temperature is exceeded in the fluid line member. An exothermic reaction might also take place below the maximum temperature when the fluid is stored for an excessively long period of time, which is e.g. often the case with dead water zones.
As a fluid particularly suited for the above-mentioned bursting insert, a molding material is used that can be spun, in particular, a spinning solution containing cellulose, water and a tertiary amine oxide, such as N-methylmorpholine N-oxide (NMMO), and stabilizers for the thermal stabilization of the cellulose and the solvent and, optionally, further additives, such as titanium dioxide, barium sulfate, graphite, carboxymethyl celluloses, polyethylene glycols, chitin, chitosan, alginic acid, polysaccharides, dyes, antibacterially acting chemicals, flameproofing agents containing phosphorus, halogens or nitrogen, activated carbon, carbon blacks or electrically conductive carbon blacks, silicic acid, organic solvents as diluents, etc. A high reaction pressure is created during a spontaneous exothermic reaction in the fluid, said pressure possibly damaging the spinning facility, in particular, pumps, fluid line members, heat exchangers, or pressure compensating tanks.
Therefore, it is known in the prior art to provide burst protection devices in the pipeline system for the case of a spontaneous exothermic reaction, said devices having the function to reduce the reaction pressure as fast as possible, thereby avoiding further damage on expensive equipment caused by the reaction pressure.
For instance, the burst protection devices of EP 0 626 198 A1, WO 94/08162 and WO 99/00185 are provided with a pressure discharge line which is closed during standard operation. Whenever a predetermined burst pressure is exceeded, which is most of the time smaller than the reaction pressure created during a spontaneous exothermic reaction, the burst protection device assumes a state in which the pressure discharge line is connected to the passage volume of the pipeline system for the fluid. Due to the volume which is now additionally available in case of bursting and thanks to the pressure discharge line, respectively, the reaction pressure in the line system can be reduced and damage to expensive equipment can be avoided.
A system having the initially mentioned features is known from EP 0 662 204 B1. The pipe described therein is provided with an over-pressure relief device the surface of which is, however, mounted in a branch. The surface of the over-pressure relief device which is shiftable under pressure is substantially flush with the inside of the wall of the pipe to avoid any deposits of the fluid on the surface. The over-pressure relief device of EP 0 662 204 B1 is designed as a bursting disc which is mounted at one end of an insert installed in the branch. The branch itself is formed by the wall of the pipeline system.
However, the apparatus of EP 0 662 204 B1 has the drawback that it is complicated to replace the bursting disc. In the apparatus of EP 0 662 204, the pressure discharge line adjacent to the bursting device must be disassembled during exchange of the bursting disc. To make the bursting disc end flush with the inner wall, an exact and complicated manufacture of the bursting disc and of the insert with exact tolerances is needed. For instance, the length of the insert in the mounted state of the bursting disc must allow for an alignment of the bursting disc with the inner wall. Moreover, the insert must be sealingly mounted in the branch.
A further drawback of the apparatus of EP 0 662 204 B1 is that there is only a very limited access to the interior of the pipe, for instance, for inspection or cleaning purposes. Finally, a further drawback of the apparatus of EP 0 662 204 B1 is that part of the wall surface of the pipe can no longer be heated due to the branch and the bursting disc. This poses problems especially when particularly large bursting discs and/or branches with a large diameter must be used because of a great distance between the individual bursting disks in the passage direction of the fluid through the pipe.
The last-mentioned drawback of the apparatus of EP 0 662 204 B1 is overcome by the development according to EP 0 789 822 B1. In the apparatus of EP 0 789 822 B1, a predetermined breaking point which will rupture when the over-pressure is reached in a pipeline is provided in the interior of the pipeline and is not part of the internal wall. It is the objective of this apparatus to permit the use of bursting discs that are as small as possible and require a minimum wall surface of the pipe wall and that do not affect, if possible, the heating of the material, which is transported through the pipeline, by the wall. A further feature of the apparatus of EP 0 789 822 B1 is that the bursting disc is definitely not positioned in the direction of flow.
However, the apparatus of EP 0 789 822 B1 still is disadvantageous in that the design is very complex. Moreover, the pressure must be discharged from the predetermined breaking point in the interior of the flow through the inner wall through a pipe projecting into the fluid. Even if the pipe projects into the flow only to a slight degree, the pipe for pressure discharge forms a flow obstacle which particularly in the case of the normally highly viscous fluids may lead to dead water zones and clogging and thus to spontaneous exothermic reactions. Moreover, an inspection of the interior of the pipe is rendered difficult because of the small diameter of the bursting disc.